Performance Evaluation of Inexpensive Cu/Fe-Based Oxygen Carriers in Chemical Looping Gasification of Coal

Solid fuel chemical looping gasification (CLG) is an innovative syngas production technology that avoids expensive air separation requirements. However, solid fuel CLG requires the development of easily available, inexpensive oxygen carrier (OC) particles with tunable reactivity and good cycling performance. In this paper, the low-cost Cu/Fe-based OCs, derived from waste ore particles and/or bauxite residues, are comprehensively evaluated for potential coal-fed CLG application in a batch fluidized bed reactor. Among these OCs, the red mud and Cu20Fe80@C (16 wt % copper ore bonded with 64 wt % hematite by 20 wt % cement) OCs exhibit better CLG performances in terms of gasification time and syngas quality. Red mud exhibits promise for the Fischer-Tropsch synthesis, while Cu20Fe80@C is in favor of the H2-rich chemical synthesis. Furthermore, coal and char gasification rates are closely related to both the lattice oxygen donation capacity and the alkali metal content in the OC, while the reduced OCs catalyze the conversion of gasification gas to the H2-rich products. In addition, the reduced OCs behave differently during the water-gas shift (WGS) and steam-iron reactions (which factually provide an approach to tune the syngas quality) in a fixed bed reactor. Reduced Cu20Fe80@C exhibits high catalytic activity toward the WGS reaction, followed by reduced Fe100@C (80 wt % hematite bonded by 20 wt % cement) and reduced red mud. With regard to the H2-rich production, the Cu20Fe80@C OC exhibits a clear advantage over red mud once both OCs experience deep reductions. Cyclic redox tests demonstrate that the red mud and Cu20Fe80@C OCs can achieve stable syngas production and exhibit good anti-sintering behavior.